Bad Piston good compression

Oct 7, 2017
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Hey I thought I blew my Piston while I was riding and when I pulled it apart there where nicks in the piston. My friend said that my ring must have broke and done that but my rings are still fully intact. Then I did a compression test and it read 120psi. Now it won't start, please help!
 
got pics of top end?
did the engine lock up or just stall?
120 psi is normal sooo what really happened:)
electrical?
fuel ?
what else have you tried?
 
got pics of top end?
did the engine lock up or just stall?
120 psi is normal sooo what really happened:)
electrical?
fuel ?
what else have you tried?
What happened was I went riding, when I was done I pulled into the garage and it was idoiling a little higher than usual so I started messing with the throttle cable and it got stuck wide open. Then I turned the key and hit the kill switch but it still was running wide opened. Then I put it in 2 and dropped the clutch to kill it. Now I can't start it. How do I post pictures?
 
Screenshot_20180201-080556.png
 
She looks beat buddy
Exactly. Lots of mechanical damage to it. What was the compression at? What's the head look like ?

Consider taking cylinder and piston to machinist to measure both to determine wear. While stock cast pistons are good, be aware that when clearance gets to much (wear) they start slapping around and will break causing MAJOR damage. IIRC cast piston needs .002" forged needs .003" .
I would avoid the temptation to put a new piston in an old hole.

IF every thing checks out good and you decide to use it as is, at least file the high spots off piston and sand high spots on the head.
 
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holy S.hit @Larry's Shee posted a link :eek:
congratulations brother:D;):cool:
and yes do not buy that kit it will do more damage to your engine and wallet
then what you have right know.
im sure you can have a shop bored the cylinder and fit a new piston which is what you need to do
NOT BUY CHEAP E-BAY CHINESE PARTS THAT WILL NOT WORK.
YAMAHA IS IN JAPAN NOT CHINAo_O
 
you should also investigate why this damage happened???
something was getting thrown around in the combustion chamber.
only time i experience that type of damage was a crank main bearing/case bearing
crapped the bed sending metal through the top end combustion chamber.
soooooo why did this damage happen inspect it before throwing money at it peaceo_O
 
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:D Thanks Speedy !! :p

Whatever it was didn't stay long. Check the reeds for lost screw.
Check exhaust, it could be in there, and get sucked back into cylinder.

Order of process:
Measure cylinder
Purchase piston
Bore/hone for final fit.
Don't use cheap gaskets. Yamaha or cometic.< Not cheap